Implement the ability to output vector fields in VTK and other formats. Currently...

Implement the ability to output vector fields in VTK and other formats. Currently, only VTK makes use of this information, but other formats may in the future. Since we now have more information that we need to write into the intermediate format output files and read back in, we also need to bump the revision number of the intermediate format by one.

Currently, there are a couple of failures in the testsuite that I will have to investigate next. There is also still a missing assertion in DataOutReader::merge that I will fix soonish.

git-svn-id: https://svn.dealii.org/trunk@15296 0785d39b-7218-0410-832d-ea1e28bc413d